Our goal is to understand the mechanisms of innate immunity at the molecular level. The innate immune system provides the body with its first line of defense against infections and is crucial for survival. Many human diseases result from a failure of the innate immune system. In order to identify and characterize novel mechanisms and effectors of the innate immune system, we will use the infections of C. elegans by several human bacterial pathogens - Pseudomonas aeruginosa, Salmonella enterica and Enterococcus faecalis - as a model. C. elegans is an excellent model for the study of innate immunity; it allows us to combine the power of genetic and functional genomic approaches to systematically and comprehensively dissect the innate immune system. For this proposal, we seek to address the following questions. Within a single organism, what are the molecules that make up the innate immune system? What intracellular pathways are triggered in response to infections by different classes of bacterial pathogens? What molecules are produced that directly destroy or inhibit the growth of the invading pathogens? We will use a variety of approaches, including the combination of genetic screens, full genome gene expression profiling, bioinformatic searches for homologous sequences known to be involved in the innate immune response, and epigenetic inhibition of gene function by double-stranded RNA interference (RNAi) to address the above questions. C. elegans has an inducible defense system and uses the evolutionarily conserved MAP kinase and TGF-beta pathways for defense against bacterial infection. The MAP kinase and TGF-beta pathways have also been implicated in innate immune response in Drosophila and in mice, respectively. Thus, we also propose to identify downstream targets to the TGF-beta pathway, and to determine how the TGF-beta pathway interacts with the MAP kinase pathway in mediating antibacterial defense. Because the signaling pathways in anti-bacterial defense are conserved across phylogeny, these studies should provide significant insights into anti-bacterial response in other organisms, including humans.